1. Field of the Invention
The present invention relates to a radiographic image capturing system for acquiring a tomographic image according to radiographic image capturing processes, and a method of displaying radiographic images.
2. Description of the Related Art
In recent years, in order for an X-ray image capturing apparatus to make a detailed observation of a local region of a subject, there has been proposed a tomosynthesis image capturing process for moving an X-ray tube over the subject while applying radiation from the X-ray tube to the subject at different angles thereby to capture radiographic images of the subject. The captured radiographic images are added together to generate a tomographic image, which is representative, with emphasis, of a desired sectional plane across the subject (see, for example, Japanese Laid-Open Patent Publication No. 57-203430).
In a tomosynthesis image capturing process, a plurality of radiographic images of a subject, which are captured at different angles, are acquired by moving an X-ray tube parallel to a detector such as a flat panel or the like, or by moving the X-ray tube along a circular or elliptical arcuate path, and the acquired radiographic images are processed to reconstruct a tomographic image of the subject. The tomographic image can be generated by translating the radiographic images, adjusting sizes of the radiographic images, and adding them together (see, for example, Japanese Laid-Open Patent Publication No. 2008-043757).
Tomosynthesis image capturing processes are disclosed in Japanese Laid-Open Patent Publication No. 2009-533086 (PCT), Japanese Laid-Open Patent Publication No. 09-313471, Japanese Laid-Open Patent Publication No. 2006-212056, and Japanese Laid-Open Patent Publication No. 2007-130487, for example.
According to the process disclosed in Japanese Laid-Open Patent Publication No. 2009-533086 (PCT), a system, which is capable of capturing both an image and a tomosynthesis image of a subject, determines the position and shape of the subject from the tomosynthesis image, and captures a CT image of the subject based on the determined position and shape of the subject.
According to the process disclosed in Japanese Laid-Open Patent Publication No. 09-313471, regions corresponding to a left-eye image and a right-eye image for three-dimensional vision (stereographic vision) are established in order to control exposure conditions for the left-eye image and the right-eye image.
According to the process disclosed in Japanese Laid-Open Patent Publication No. 2006-212056, transmissive radiographic images, which have been captured, are processed in order to reconstruct a three-dimensional image. After parameters are extracted from the three-dimensional image, positions of a radiation source for capturing images for stereographic vision are determined, and then the images are captured.
According to the process disclosed in Japanese Laid-Open Patent Publication No. 2007-130487, a pair of projected images extracted from a tomographic projection data set are used as a left-eye image and a right-eye image for stereographic vision. Japanese Laid-Open Patent Publication No. 2007-130487 describes the usefulness of an observation process based on stereographic vision, stating that a three-dimensional observation process, i.e., an observation process based on stereographic vision, is useful during observation of radiographic images because the process can provide clues concerning distance or depth, in the same manner as human eyes in a normal process of visual perception, and hence can clarify relative spatial relationships between objects in a subject's body.
The process disclosed in Japanese Laid-Open Patent Publication No. 2009-533086 (PCT) is problematic in that the dose of radiation applied to the subject is large because it is necessary to perform a tomosynthesis image capturing process on the subject prior to a CT image capturing process.
Japanese Laid-Open Patent Publication No. 09-313471 discloses a process of capturing radiographic images for producing images for observation based on stereographic vision. If a tomographic image is generated separately from images for stereographic vision, then it is necessary to perform a radiographic image capturing process in order to produce the tomographic image. In this case, the dose of radiation applied to the subject increases.
The process disclosed in Japanese Laid-Open Patent Publication No. 2006-212056 also is disadvantageous in that, after a radiographic image capturing process has been performed to produce a three-dimensional image, image capturing conditions for stereographic vision are determined based on information of the three-dimensional image, and then a radiographic image capturing process for stereographic vision is carried out. Therefore, the dose of radiation applied to the subject also increases.
The process disclosed in Japanese Laid-Open Patent Publication No. 2007-130487 is able to solve problems encountered using the processes disclosed in Japanese Laid-Open Patent Publication No. 2009-533086 (PCT), Japanese Laid-Open Patent Publication No. 09-313471, and Japanese Laid-Open Patent Publication No. 2006-212056, because the process disclosed in Japanese Laid-Open Patent Publication No. 2007-130487 uses a pair of radiographic images extracted from tomographic image data.
However, according to the process disclosed in Japanese Laid-Open Patent Publication No. 2007-130487, the pair of radiographic images are simply selected and displayed. There is no specific technique relating to extraction and display of radiographic images for stereographic vision when the operator wants to confirm a lesion area by away of stereographic vision, after having first confirmed a tomographic image. Therefore, the disclosed process is disadvantageous in that it is inconvenient for viewing images by way of stereographic vision.